Poisoned waters: Laguna de Bay’s steady crawl to brink of disaster

May 22, 2024

(Part 1 of 2)

MANILA, Philippines — Encircled by the contrast of verdant and urban landscapes, Laguna de Bay is a silent witness to the environmental tug-of-war between progress and preservation, with few actors playing by the rules.

Nestled in the heart of the Philippines, Laguna de Bay — often casually referred to as Laguna Lake — holds the distinction of being the nation’s largest freshwater lake and ranks as the third-largest in Southeast Asia by surface area.

Historically, the lake has shown remarkable ecological resilience. Despite past predictions warning that it could become biologically dead in 10 to 15 years, it has consistently managed to heal itself, mainly due to its natural self-cleansing ability akin to that of other robust lake ecosystems.

Those days seem to be over.

A six-month investigation into the contamination of Laguna de Bay has exposed a series of regulatory failures and lack of transparency about who is behind the pollution and what the authorities are doing to stop it.

Analysis of data provided by independent scientific sources reveals a troubling trend: Laguna de Bay is grappling with increased fecal contamination, which threatens to disrupt its ecological equilibrium.

This pollution rise not only jeopardizes public health but also imperils the lake’s rich biodiversity and the livelihood of countless communities that rely on its resources.

The government agency tasked with keeping the lake clean and safe has refused to share data on citations against polluters or make regular internal water quality readings public. The Commission on Audit (COA) has criticized the Laguna Lake Development Authority (LLDA) for failure to collect rent and regulatory fees that would fund proper oversight and monitoring.

In the first part of this investigation, we will analyze the quality of water in the lake, investigate the history of the LLDA, and examine the composition of waste found in the lake.

In the second part, we will delve into the sources and impacts of pollution, including its effects on tributaries and the lake itself, as well as the consequences for surrounding communities.

A troubled agency oversees troubled waters

Since its establishment in 1969, the LLDA has several times faced criticism as pollution in the lake reached critical levels.

Often the data driving the criticism has come from external scientific studies since the LLDA is often reluctant to share its data, though even its own monitoring data is causing renewed concern about the fate of the lake.

Under the Department of Environment and Natural Resources (DENR) Administrative Order No. 34 Series of 1990, Laguna de Bay is designated as a Class C water body, supporting fisheries, recreational activities, and agriculture. The LLDA is supposed to ensure it maintains that status through monitoring and management.

Despite its Class C status, Laguna de Bay is feared to go the way of Pasig River — a vital waterway connecting Laguna de Bay to Manila Bay — that was declared biologically dead due to unregulated pollution by humans and industry.

Since the late 1990s, environmentalists have raised concerns about conditions in the lake and the LLDA’s ability to do anything about it.

A 1998 article from OneOcean.org, referencing a study from 1985, pointed to alarmingly high coliform levels, with Dr. Carlito Barril, now retired dean of the University of the Philippines College of Sciences, describing the lake as “a very, very big septic tank.”

This study found that fecal coliform levels in the lake reached a staggering 2 million MPN/100 ml, a figure that is 10,000 times the current maximum allowable limit for Class C water bodies — set at a maximum of 200 MPN/100 ml — based on DENR Water Quality Guidelines No. 2021-19.

While there have been some improvements in the water quality of Laguna de Bay since the 1980s, recent monitoring data reveal that pollution issues, especially concerning fecal coliform contamination, persistently plague the lake.

The LLDA is charged with managing Laguna de Bay, the largest freshwater lake in the Philippines, balancing economic activities with environmental preservation.

Established under Republic Act No. 4850, LLDA’s responsibilities include water resource management, pollution control, and sustainable development of the surrounding areas. Funded by government allocations and its own revenue from permits and fines, the agency enforces environmental laws and regulates activities around the lake.

The LLDA has the authority to issue cease and desist orders and notices of violations to combat pollution. However, concerns about transparency persist as the agency has been reticent about releasing details on the entities it penalizes and has denied all of the Freedom of Information (FOI) requests submitted for this investigation.

A lake awash in human and animal waste

People on the frontlines of the contamination of Laguna de Bay are the fishermen. On a brisk morning along the shores of Laguna de Bay in Muntinlupa City, the strong winds stirred the waters into vigorous waves, noticeable even from the Lake Management Office (LMO) built on stilts and mainly bamboo.

Here, veteran fisherman Ronaldo Molera, 65, reflected on the deteriorating water quality he’s observed over five decades. He noted a significant drop in fish catch, a trend he attributes to pollution alongside illegal fishing.

“Ang tingin ko nagpapababa [ng fish production] bukod sa illegal fishing ay ‘yung pollution na. Bumaba po ‘yung kalidad ng tubig ng lawa. Itong sinasabi ko base sa experience namin, sa mga nakikita namin,” he told INQUIRER.net.

(I think what’s lowering [fish production] aside from illegal fishing is the pollution. The water quality of the lake has declined. What I’m saying is based on our experience and what we see.)

A creek within a Muntinlupa City barangay is choked with garbage and assorted debris. According to local residents, the majority of this waste originates from neighboring cities, ultimately accumulating in their creek’s trash traps.Photo by Cristina Eloisa Baclig

Amid the scenic vistas of Laguna de Bay, analysis of water quality data from the LLDA reveals a less picturesque reality.

In 2021, Station 19, located in Muntinlupa, reported a staggering spike in fecal coliform levels, reaching 945.8 MPN/100 ml. This figure not only exceeds the standard for Class C water bodies but also represents an alarming surge from previous years, pointing to a concerning rise in water pollution.

For those living around Laguna de Bay, the term “fecal coliform” might sound technical, but it essentially refers to bacteria from human and animal waste.

Engineer Jocelyn Sta. Ana, division chief III of the Environmental Laboratory and Research Division (ELRD) of LLDA, explained that when these bacteria levels are high, it’s a sign that untreated sewage is ending up in the lake.

To visualize the extent of contamination, consider this: the fecal coliform level at Station 19 in Muntinlupa is like having nearly five 55-gallon drums of water, with each drum containing water that has coliform levels almost five times above the acceptable threshold for Class C waters.

In an interview, Sta. Ana clarified the 2021 fecal coliform data, stressing the absence of saltwater intrusion, a natural phenomenon that typically helps to dilute fecal contamination.

“For 2021 and 2022, we did not experience saltwater intrusion, which often helps to mitigate fecal contamination levels naturally,” she explained, speaking in a mixture of Filipino and English.

“Our observations also suggest that when saltwater does intrude, depending on its extent, there’s a noticeable decrease in fecal coliform levels,” she added.

Sta. Ana said that with the vastness of Laguna de Bay, not all areas are equally affected by this natural cleansing process.

“The saltwater mostly enters the West Bay, influenced by currents and flow, occasionally reaching as far as the Central Bay via the Diablo Pass, where it can get trapped, creating higher chloride concentrations in some areas compared to others,” Sta. Ana adds.

The Diablo Pass — also known as Devil’s Pass — the lake’s deepest part at 20 meters, sits to the northeast of Muntinlupa Station. It is a vital marine channel between Talim Island and the mainland of Binangonan and Cardona in Rizal province.

The Pass’s dynamics affect the distribution and concentration of pollutants, but its deeper waters and the contours of the lake bed can trap contaminants, affecting coliform levels.

“The dynamics are complex, with a confluence of factors at play within the Laguna de Bay environment,” Sta. Ana continued.

Data from 2021 tell a concerning story, where not only Muntinlupa’s station but others as well grapple with spikes in contamination.

Station 15 in San Pedro (West Bay) reported a significant increase to 337.3 MPN/100ml, while Station XX, known as GEMS, showed a jump to 617.7 MPN/100ml.

This time, instead of industrial oil drums, envision a typical backyard swimming pool. Its sheer volume of water becomes a stark canvas illustrating the fecal coliform problem.

Data from Station 15, equating to 337.3 MPN/100ml, would be akin to having two such pools, each indicative of the troubling coliform levels.

At the GEMS station, with a count of 617.7 MPN/100ml, imagine the scenario extending to more than three pools, highlighting the extent of contamination far beyond the safety standards for Class C waters.

The significant spikes observed in monitoring stations across Muntinlupa, West Bay, and GEMS station in 2021 undeniably raise alarm bells for residents and environmentalists alike, painting a stark picture of the lake’s water quality challenges.

However, in discussions with the LLDA, a somewhat different perspective emerges. Officials there acknowledge the 2021 spikes but also point to a natural capacity of the lake’s ecosystem to rehabilitate itself.

Finding out what is really in the water

While the LLDA has not offered an analysis of why water contamination levels are so high, others have been at work trying to identify exactly what is in the water. At the University of the Philippines (UP) Diliman, researchers have been piecing together a puzzle that has long troubled the waters of Laguna de Bay.

Through a meticulous process known as DNA fingerprinting, they’ve uncovered hard data on what’s been affecting the lake’s water quality: a significant portion of the contamination comes from human sewage and agricultural waste. Both the tributaries flowing into the lake and the lake itself are directly contaminated.

Rowena Pagdingalan, an engineer from the Surveillance and Monitoring Division of LLDA, sheds light on the local angle.

“Most of our homes use septic tanks. When these tanks overflow, the untreated waste can find its way back into our environment. This is especially concerning because, unlike in large treatment facilities, we don’t have processes like chlorination in our homes to treat this waste,” she said.

This domestic dilemma is echoed in the findings of a 2021 study. It points to sewage as the major source of the lake’s fecal contamination, a fact that’s not only unsavory but carries real risks of waterborne diseases for the communities relying on the lake.

“Fecal pollution due to sewage may be due to the inadequate wastewater treatment system in the Philippines,” the study said.

In Metro Manila, the heart of the problem is that only 15% of homes are connected to a sewage system, and of those, only half are treated properly. In areas where houses are tightly packed and informal, the problem is even more pressing. There, wastewater often goes straight into drains with no treatment at all.

“The presence of fecal coliform in water or any water bodies indicates that sewage systems are being contaminated with fecal matter,” said Dr. Rico Ancog, dean of the School of Environmental Science and Management at the University of the Philippines (UP) Los Baños.

“In the case of the Laguna de Bay, the presence of fecal coliform highly indicates effluents coming from various sources such as sewage in urban areas and industrial plants, and agricultural run-offs,” he explained.

In Muntinlupa, where a huge spike in fecal coliform levels was recorded in 2021, previous census data indicated that a significant number of the city’s residents are without basic household necessities, including essential appliances and access to clean water.

Critically, 15 percent of the city’s poorest population faces a severe lack of proper sanitation facilities, such as working toilets, alongside inadequate waste disposal services.

According to Benjie Reyes, president of the Barangay Fisheries and Aquatic Resource Management Council (BFARMC) in Barangay Bayanan in Muntinlupa City, several areas along the lakeshore have been occupied by informal settlers.

Reyes noted that informal dwellers typically reside in bamboo houses perched on stilts over contaminated waters, and many of these homes lack a functioning or proper toilet.

When asked if he believed the informal settlers and inadequate sewage systems were responsible for the high fecal coliform levels in Muntinlupa, Reyes expressed uncertainty:

“Well, I’m not really sure. It really depends on where they’re testing. If they do the testing out in the deeper parts [of the lake], it’s really clean there, but you can’t say the same for the areas near the shore because there are canals there,” he said.

Laguna de Bay’s biological struggle to clean itself

Though the contamination levels are not in dispute, the resiliency of the lake is something that scientists continue to debate even as contamination levels continue to rise.

Sta. Ana, with tempered optimism, acknowledged the increase in fecal coliform levels, particularly in the Muntinlupa area of Laguna de Bay, noting the significance as this is where water concessionaire Maynilad sources water for distribution to households in Muntinlupa and other areas after treatment.

She emphasized the treatability of fecal coliform, stating: “At the level of Laguna Lake now, it’s still easy to treat. Sunlight also has an effect on them; it can help reduce levels because sunlight has UV rays, so it can also lower the level.”

“It’s not persistent, it’s not cumulative. For example, when it reaches 1,000, there’s a flow. It won’t keep adding up because these bacteria have a life, and at a certain level, in specific conditions, they eventually die. It’s not that they keep increasing and accumulating,” she explained.

Ancog is less optimistic.

“[T]he presence of such high coliform counts, regardless of subsequent decreases, should not be downplayed as it indicates underlying pollution issues that need addressing,” Ancog stressed.

“For saltwater intrusion, the time it takes to cleanse fecal coliform in the lake widely depends on various environmental parameters such as the concentration of fecal coliform, temperature, rate of water flow, and other biological processes,” he told INQUIRER.net.

“The effectiveness of these methods [to reduce fecal coliform counts in the lake] (saltwater intrusion, disinfection, effect of sunlight, UV, and chlorination) vary on various conditions and factors such as the severity of contamination, rate of water flow, local environmental conditions, and other biological parameters,” he added.

Further analysis of monitoring station data showed that in the Muntinlupa Station, there was a notable decrease in coliform levels from 2021 to 2022, which may indicate that the lake’s environmental dynamics provide some self-correcting mechanisms.

Despite the observed reductions, the substantial presence of fecal coliform in 2021 is a reminder of the lake’s susceptibility to pollution.

“[I]t’s still an indication of pollution. But for now, because the lake is flowing, it’s not like other lakes that are stagnant. [I]t has inflow and outflow so other pollutants can be discharged to the Pasig River, while others undergo cleansing within the lake itself,” Sta. Ana argued.

On the other hand, Ancog stressed that “the presence of such high coliform counts, regardless of subsequent decreases, should not be downplayed as it indicates underlying pollution issues that need addressing.”

Not in dispute is that if rates of contamination continue to rise, the lake will not be able to continue to thrive.

Our investigation indicates that the real culprits lie along the tributaries pouring into the lake. In order to identify where the sewage is coming from and the efforts to hold local authorities accountable, we went to the source. Read more in Part 2.

Reporting for this story was supported by the Environmental Data Journalism Academy – a program of Internews’ Earth Journalism Network and Thibi.


Fecal coliform data were acquired from the Laguna Lake Development Authority reports covering January 2018 to December 2022. Data for April to August 2020 were unavailable as a result of pandemic restrictions. Data for November 2020 were unavailable because of power interruptions caused by Typhoon Ulysses.

A complete list of the steps taken in scraping, cleaning, and analyzing fecal coliform level data can be found on the Data Diary sheet of the DataDoc on Laguna de Bay fecal coliform analysis.

This report also used data on the sources of fecal contamination in Laguna de Bay from a study by Windell L. Rivera, et. al, published online in the Journal of Water & Health by the International Water Association.

  • Story Mentors: Karol Ilagan, Eva Constantaras
  • Data Mentor: Thet Paing Myo
  • Editors: Tony Bergonia, Eva Constantaras